Semiconductor device and method for fabricating the same

ABSTRACT

A semiconductor device includes a substrate having a first region and a second region, a first fin-shaped structure extending along a first direction on the first region, a double diffusion break (DDB) structure extending along a second direction to divide the first fin-shaped structure into a first portion and a second portion, and a first gate structure and a second gate structure extending along the second direction on the DDB structure.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 17/140,157, filed on Jan. 4, 2021. The content of the application isincorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to a method for fabricating semiconductor device,and more particularly to a method for dividing fin-shaped structure toform single diffusion break (SDB) structure.

2. Description of the Prior Art

With the trend in the industry being towards scaling down the size ofthe metal oxide semiconductor transistors (MOS), three-dimensional ornon-planar transistor technology, such as fin field effect transistortechnology (FinFET) has been developed to replace planar MOStransistors. Since the three-dimensional structure of a FinFET increasesthe overlapping area between the gate and the fin-shaped structure ofthe silicon substrate, the channel region can therefore be moreeffectively controlled. This way, the drain-induced barrier lowering(DIBL) effect and the short channel effect are reduced. The channelregion is also longer for an equivalent gate length, thus the currentbetween the source and the drain is increased. In addition, thethreshold voltage of the fin FET can be controlled by adjusting the workfunction of the gate.

In current FinFET fabrication, after shallow trench isolation (STI) isformed around the fin-shaped structure part of the fin-shaped structureand part of the STI could be removed to form a trench, and insulatingmaterial is deposited into the trench to form single diffusion break(SDB) structure or isolation structure. However, the integration of theSDB structure and metal gate fabrication still remains numerousproblems. Hence how to improve the current FinFET fabrication andstructure has become an important task in this field.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention, a semiconductordevice includes a substrate having a first region and a second region, afirst fin-shaped structure extending along a first direction on thefirst region, a double diffusion break (DDB) structure extending along asecond direction to divide the first fin-shaped structure into a firstportion and a second portion, and a first gate structure and a secondgate structure extending along the second direction on the DDBstructure.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view illustrating a method for fabricating asemiconductor device according to an embodiment of the presentinvention.

FIGS. 2-7 are cross-section views illustrating a method for fabricatinga semiconductor device according to an embodiment of the presentinvention.

DETAILED DESCRIPTION

Referring to FIGS. 1-2, in which FIG. 1 is a top view illustrating amethod for fabricating a semiconductor device according to an embodimentof the present invention, the left portion of FIG. 2 illustrates across-sectional view of FIG. 1 for fabricating the semiconductor devicealong the sectional line AA′, and the right portion of FIG. 2illustrates a cross-sectional view of FIG. 1 for fabricating thesemiconductor device along the sectional line BB′. As shown in FIGS.1-2, a substrate 12, such as a silicon substrate or silicon-on-insulator(SOI) substrate is first provided, a first region such as a NMOS region14 and a second region such as a PMOS region 16 are defined on thesubstrate 12, and at least a fin-shaped structure 18 is formed on eachof the NMOS region 14 and PMOS region 16. It should be noted that eventhough four fin-shaped structures 18 are disposed on each of thetransistor regions in this embodiment, it would also be desirable toadjust the number of fin-shaped structures 18 depending on the demand ofthe product, which is also within the scope of the present invention.

Preferably, the fin-shaped structures 18 of this embodiment could beobtained by a sidewall image transfer (SIT) process. For instance, alayout pattern is first input into a computer system and is modifiedthrough suitable calculation. The modified layout is then defined in amask and further transferred to a layer of sacrificial layer on asubstrate through a photolithographic and an etching process. In thisway, several sacrificial layers distributed with a same spacing and of asame width are formed on a substrate. Each of the sacrificial layers maybe stripe-shaped. Subsequently, a deposition process and an etchingprocess are carried out such that spacers are formed on the sidewalls ofthe patterned sacrificial layers. In a next step, sacrificial layers canbe removed completely by performing an etching process. Through theetching process, the pattern defined by the spacers can be transferredinto the substrate underneath, and through additional fin cut processes,desirable pattern structures, such as stripe patterned fin-shapedstructures could be obtained.

Alternatively, the fin-shaped structures 18 could also be obtained byfirst forming a patterned mask (not shown) on the substrate, 12, andthrough an etching process, the pattern of the patterned mask istransferred to the substrate 12 to form the fin-shaped structures 18.Moreover, the formation of the fin-shaped structures 18 could also beaccomplished by first forming a patterned hard mask (not shown) on thesubstrate 12, and a semiconductor layer composed of silicon germanium isgrown from the substrate 12 through exposed patterned hard mask viaselective epitaxial growth process to form the corresponding fin-shapedstructures 18. These approaches for forming fin-shaped structure are allwithin the scope of the present invention. It should be noted that afterthe fin-shaped structures 18 are formed, a liner 22 made of siliconoxide could be formed on the surface of the fin-shaped structures 18 onthe NMOS region 14 and PMOS region 16.

Next, a shallow trench isolation (STI) 20 is formed around thefin-shaped structures 18. In this embodiment, the formation of the STI20 could be accomplished by conducting a flowable chemical vapordeposition (FCVD) process to form a silicon oxide layer on the substrate12 and covering the fin-shaped structures 18 entirely. Next, a chemicalmechanical polishing (CMP) process along with an etching process areconducted to remove part of the silicon oxide layer so that the topsurface of the remaining silicon oxide is slightly lower than the topsurface of the fin-shaped structures 18 for forming the STI 20.

Next, as shown in FIG. 2, an etching process is conducted by using apatterned mask (not shown) as mask to remove part of the liner 22 andpart of the fin-shaped structures 18 to form trenches 24, in which eachof the trenches 24 preferably divides each of the fin-shaped structures18 disposed on the NMOS region 14 and PMOS region 16 into two portions,including a portion 26 on the left side of the trench 24 and a portion28 on the right side of the trench 24. In this embodiment, the width ofthe trench 24 on the NMOS region 14 is preferably greater than the widthof the trench 24 on the PMOS region 16. Nevertheless, according to otherembodiment of the present invention, it would also be desirable toadjust the width of the trenches 24 on both NMOS region 14 and PMOSregion 16 so that the trenches 24 on both region 14, 16 could have samewidths or different widths, which are all within the scope of thepresent invention.

Next, as shown in FIG. 3, an oxidation process is conducted to formanother liner 30 made of silicon oxide in the trenches 24 on the NMOSregion 14 and PMOS region 16, in which the liner 30 is disposed on thebottom surface and two sidewalls of the trenches 24 and contacting theliner 22 directly. Next, a dielectric layer 32 is formed in the trenches24 and filling the trenches 24 completely, and a planarizing processsuch as chemical mechanical polishing (CMP) process and/or etchingprocess is conducted to remove part of the dielectric layer 32 so thatthe top surface of the remaining dielectric layer 32 is even with orslightly higher than the top surface of the fin-shaped structures 18.This forms a double diffusion break (DDB) structure 34 on the NMOSregion 14 and a SDB structure 34 on the PMOS region 16 at the same time.

Preferably, two gate structures will be formed on the DDB structure 34in the later process whereas only a single gate structure will be formedon the SDB structure 36. As shown in FIG. 1, each of the fin-shapedstructures 18 on the NMOS region 14 and PMOS region 16 are disposedextending along a first direction (such as X-direction) while the DDBstructure 34 and the SDB structure 36 are disposed extending along asecond direction (such as Y-direction), in which the first direction isorthogonal to the second direction.

It should be noted that the dielectric layer 32 and the liner 30 in thisembodiment are preferably made of different materials, in which theliner 30 is preferably made of silicon oxide and the dielectric layer 32is made of silicon oxycarbonitride (SiOCN). Specifically, the DDBstructure 34 and the SDB structure 36 made of SiOCN in this embodimentare preferably structures having low stress, in which the concentrationproportion of oxygen within SiOCN is preferably between 30% to 60% andthe stress of each of the DDB structure 34 and the SDB structure 36 isbetween 100 MPa to −500 MPa or most preferably at around 0 MPa. Incontrast to the conventional DDB or SDB structures made of dielectricmaterial such as silicon oxide or silicon nitride, the SDB structures ofthis embodiment made of low stress material such as SiOCN could increasethe performance of on/off current in each of the transistors therebyboost the performance of the device.

Next, as shown in FIG. 4, an ion implantation process could be conductedto form deep wells or well regions in the fin-shaped structures 18 onthe NMOS region 14 and PMOS region 16, and a clean process could beconducted by using diluted hydrofluoric acid (dHF) to remove the liner22 on the surface of the fin-shaped structures 18 completely, part ofthe liner 30 on sidewalls of the trenches 24, and even part of the DDBstructure 34 and the SDB structure 36. This exposes the surface of thefin-shaped structures 18 and the top surfaces of the remaining liner 30,the DDB structure 34, and the SDB structure 36 are slightly lower thanthe top surface of the fin-shaped structures 18 while the top surface ofthe DDB structure 34 and the SDB structure 36 is also slightly higherthan the top surface of the remaining liner 30.

Next, as shown in FIG. 5, at least a gate structure such as gatestructures 38, 40, 74 or dummy gates are formed on the fin-shapedstructures 18 on the NMOS region 14 and PMOS region 16. In thisembodiment, the formation of the first gate structure 38, 40, 74 couldbe accomplished by a gate first process, a high-k first approach fromgate last process, or a high-k last approach from gate last process.Since this embodiment pertains to a high-k last approach, a gatedielectric layer 42 or interfacial layer, a gate material layer 44 madeof polysilicon, and a selective hard mask could be formed sequentiallyon the substrate 12 or fin-shaped structures 18, and a photo-etchingprocess is then conducted by using a patterned resist (not shown) asmask to remove part of the gate material layer 44 and part of the gatedielectric layer 42 through single or multiple etching processes. Afterstripping the patterned resist, gate structures 38, 40, 74 each composedof a patterned gate dielectric layer 42 and a patterned material layer44 are formed on the fin-shaped structures 18.

It should be noted that the formation of the gate structures 38, 40, 74by patterning the gate material layer 44 could be accomplished by asidewall image transfer (SIT) process. For instance, a plurality ofpatterned sacrificial layers or mandrels having same widths and samedistance therebetween could be formed on the gate material layer 44 andthen deposition and etching process could be conducted to form spacerson sidewalls of the patterned sacrificial layers. After removing thepatterned sacrificial layers, the pattern of the spacers is thentransferred to the gate material layer 44 for forming gate structures38, 40, 74. In this embodiment, two gate structures 38, 40 are formed onthe DDB structure 34 on NMOS region 16 while only a single gatestructure 74 is formed on the SDB structure 36 on PMOS region 14, inwhich the width of each of the gate structures 38, 40 on the NMOS region16 is substantially equal to the width of the gate structure 74 on thePMOS region 14. Nevertheless, according to other embodiment of thepresent invention, it would also be desirable to adjust the sizeincluding widths of the gate structures 38, 40, 74 during the formationof the gate structures 38, 40, 74 so that the width of each of the gatestructures 38, 40 on the NMOS region 14 could be less than or greaterthan the width of the gate structure 74 on the PMOS region 16, which areall within the scope of the present invention.

Next, at least a spacer 46 is formed on sidewalls of the each of thegate structures 38, 40, 74, a source/drain region 48 and/or epitaxiallayer 50 is formed in the fin-shaped structure 18 adjacent to two sidesof the spacer 46, and selective silicide layers (not shown) could beformed on the surface of the source/drain regions 48. In thisembodiment, each of the spacers 46 could be a single spacer or acomposite spacer, such as a spacer including but not limited to forexample an offset spacer and a main spacer. Preferably, the offsetspacer and the main spacer could include same material or differentmaterial while both the offset spacer and the main spacer could be madeof material including but not limited to for example SiO₂, SiN, SiON,SiCN, or combination thereof. The source/drain regions 48 and epitaxiallayers 50 could include different dopants and/or different materialsdepending on the conductive type of the device being fabricated. Forinstance, the source/drain region 48 on the NMOS region 14 could includen-type dopants and the epitaxial layer 50 on the same region couldinclude silicon phosphide (SiP) while the source/drain region 48 on thePMOS region 16 could include p-type dopants and the epitaxial layer 50on the same region could include silicon germanium (SiGe). It should benoted that since the spacers 46 and the DDB structure 34 on the NMOSregion 14 could be made of same material including but not limited tofor example silicon oxide or silicon nitride, part of the DDB structure34 could be removed to form at least a protrusion 76 between the twogate structures 38, 40 when deposition and etching back processes wereconducted to form the spacers 46.

Next, as shown in FIG. 6, a contact etch stop layer (CESL) 52 is formedon the surface of the fin-shaped structures 18 and covering the gatestructures 38, 40, 74, and an interlayer dielectric (ILD) layer 54 isformed on the CESL 52. Next, a planarizing process such as CMP isconducted to remove part of the ILD layer 54 and part of the CESL 52 forexposing the gate material layer 44 made of polysilicon, in which thetop surface of the gate material layer 44 is even with the top surfaceof the ILD layer 54.

Next, a replacement metal gate (RMG) process is conducted to transformthe gate structures 38, 40, 74 into metal gates 60. For instance, theRMG process could be accomplished by first performing a selective dryetching or wet etching process using etchants including but not limitedto for example ammonium hydroxide (NH₄OH) or tetramethylammoniumhydroxide (TMAH) to remove the gate material layer 44 and even gatedielectric layer 42 from the gate structures 38, 40, 74 for formingrecesses 56 in the ILD layer 54.

Next, as shown in FIG. 7, a selective interfacial layer or gatedielectric layer 62, a high-k dielectric layer 64, a work function metallayer 66, and a low resistance metal layer 68 are formed in the recesses56, and a planarizing process such as CMP is conducted to remove part oflow resistance metal layer 68, part of work function metal layer 66, andpart of high-k dielectric layer 64 to form metal gates 60. Next, part ofthe low resistance metal layer 68, part of the work function metal layer66, and part of the high-k dielectric layer 64 are removed to form arecess (not shown) on each of the transistor region, and a hard mask 70made of dielectric material including but not limited to for examplesilicon nitride is deposited into the recesses so that the top surfacesof the hard mask 70 and ILD layer 54 are coplanar. In this embodiment,each of the gate structures or metal gates 60 fabricated through high-klast process of a gate last process preferably includes an interfaciallayer or gate dielectric layer 62, a U-shaped high-k dielectric layer64, a U-shaped work function metal layer 66, and a low resistance metallayer 68.

In this embodiment, the high-k dielectric layer 64 is preferablyselected from dielectric materials having dielectric constant (k value)larger than 4. For instance, the high-k dielectric layer 64 may beselected from hafnium oxide (HfO₂), hafnium silicon oxide (HfSiO₄),hafnium silicon oxynitride (HfSiON), aluminum oxide (Al₂O₃), lanthanumoxide (La₂O₃), tantalum oxide (Ta₂O₅), yttrium oxide (Y₂O₃), zirconiumoxide (ZrO₂), strontium titanate oxide (SrTiO₃), zirconium silicon oxide(ZrSiO₄), hafnium zirconium oxide (HfZrO₄), strontium bismuth tantalate(SrBi₂Ta₂O₉, SBT), lead zirconate titanate (PbZr_(x)Ti_(1-x)O₃, PZT),barium strontium titanate (Ba_(x)Sr_(1-x)TiO₃, BST) or a combinationthereof.

In this embodiment, the work function metal layer 66 is formed fortuning the work function of the metal gate in accordance with theconductivity of the device. For an NMOS transistor, the work functionmetal layer 66 having a work function ranging between 3.9 eV and 4.3 eVmay include titanium aluminide (TiAl), zirconium aluminide (ZrAl),tungsten aluminide (WAl), tantalum aluminide (TaAl), hafnium aluminide(HfAl), or titanium aluminum carbide (TiAlC), but it is not limitedthereto. For a PMOS transistor, the work function metal layer 66 havinga work function ranging between 4.8 eV and 5.2 eV may include titaniumnitride (TiN), tantalum nitride (TaN), tantalum carbide (TaC), but it isnot limited thereto. An optional barrier layer (not shown) could beformed between the work function metal layer 66 and the low resistancemetal layer 68, in which the material of the barrier layer may includetitanium (Ti), titanium nitride (TiN), tantalum (Ta) or tantalum nitride(TaN). Furthermore, the material of the low-resistance metal layer 68may include copper (Cu), aluminum (Al), titanium aluminum (TiAl), cobalttungsten phosphide (CoWP) or any combination thereof.

Next, a pattern transfer process is conducted by using a patterned mask(not shown) as mask to remove part of the ILD layer 54 and part of theCESL 52 for forming contact holes (not shown) exposing the source/drainregions 48 underneath. Next, metals including a barrier layer selectedfrom the group consisting of Ti, TiN, Ta, and TaN and a low resistancemetal layer selected from the group consisting of W, Cu, Al, TiAl, andCoWP are deposited into the contact holes, and a planarizing processsuch as CMP is conducted to remove part of aforementioned barrier layerand low resistance metal layer for forming contact plugs 72 electricallyconnecting the source/drain regions 48. This completes the fabricationof a semiconductor device according to a preferred embodiment of thepresent invention.

It should be noted that even though a SIT scheme is employed to form thegate structures 38, 40, 74 on NMOS region 14 and PMOS region 16respectively, according to other embodiment of the present invention, itwould also be desirable to first form gate structures and spacers havingequal widths on NMOS region 14 and PMOS region 16 at the same time,remove the gate structure made of polysilicon on the NMOS region 14 sothat the remaining spacer could be used as a sacrificial gate structure,and then form new spacer on sidewalls of the sacrificial gate structureon the NMOS region 14. Next, RMG process conducted from FIGS. 6-7 couldbe carried out to transform the sacrificial or dummy gate structureoriginally made from spacer on NMOS region 14 and the gate structuremade from polysilicon on PMOS region 16 to metal gates. In thisapproach, since the metal gate on the NMOS region 14 is transformed fromspacer, the width of the final metal gate formed on NMOS region 14 wouldbe equal to the width of the spacer on each sidewall of the gatestructure 74 on PMOS region 16.

Referring to FIG. 7, FIG. 7 further illustrates a structural view of asemiconductor device according to an embodiment of the presentinvention. As shown in FIG. 7, the semiconductor device includes a DDBstructure 34 disposed on the NMOS region 14 for dividing the fin-shapedstructure 18 on the NMOS region 14 into two portions including portions26 and 28 adjacent to two sides of the DDB structure 34, gate structures38 and 40 disposed on the DDB structure 34, a SDB structure 36 disposedon the PMOS region 16 for dividing the fin-shaped structure 18 on thePMOS region 16 into two portions including portions 26 and 28 adjacentto two sides of the SDB structure 36, and a single gate structure 74disposed on the SDB structure 36.

In this embodiment, the two gate structures 38, 40 disposed on the DDBstructure 34 preferably overlap the fin-shaped structure 18 and the DDBstructure 34 at the same time. For instance, the left gate structure 38is disposed to overlap or stand on the fin-shaped structure 18 on theleft and part of the DDB structure 34 at the same time while the rightgate structure 40 is disposed to overlap the fin-shaped structure 18 onthe right and part of the DDB structure 34 at the same time. Preferably,the bottom surfaces of the gate structures 38, 40 disposed directly onthe DDB structure 34 are slightly lower than the top surface of thefin-shaped structure 18 on two adjacent sides. Specifically, the DDBstructure 34 also includes a protrusion 76 protruding from the topsurface of the DDB structure 34 and between the two gate structures 38,40, in which the top surface of the protrusion 76 could be slightlylower than, even with, or higher than the top surface of the fin-shapedstructure 18.

Only a single gate structure 74 however is disposed on top of the SDBstructure 36 on the PMOS region 16, in which the bottom surface of thegate structure 74 is preferably lower than the top surface of thefin-shaped structure 18 on two adjacent sides as the gate structure 74is standing on the fin-shaped structure 18 and the SDB structure 36 atthe same time. Preferably, the width of each of the gate structures 38,40 on the DDB structure 34 could be less than, equal to, or greater thanthe width of the gate structure 74 disposed on the SDB structure 36, thewidth of either bottom surface or top surface of the DDB structure 34could be less than, equal to, or greater than the width of bottomsurface or top surface of the SDB structure 36, and the top surface ofthe DDB structure 34 excluding the protrusion 76 could be lower than,even with, or higher than the top surface of the SDB structure 36, whichare all within the scope of the present invention.

Overall, the present invention provides an approach for integrating DDBstructure and SDB structure for accommodating tensile stress applied onNMOS devices and compressive stress applied on PMOS devices, in which aDDB structure is formed on the NMOS region while a SDB structure isformed on the PMOS region. Structurally, the top surface of both the DDBstructure and SDB structure is slightly lower than the top surface offin-shaped structures on two adjacent sides, two gate structures aredisposed on the DDB structure and fin-shaped structures on two adjacentsides at the same time, a protrusion is formed on the top surface of theDDB structure and between the two gate structures, and only a singlegate structure is disposed on the SDB structure and fin-shapedstructures on two adjacent sides.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A semiconductor device, comprising: a substratehaving a first region and a second region; a first fin-shaped structureextending along a first direction on the first region; a doublediffusion break (DDB) structure extending along a second direction todivide the first fin-shaped structure into a first portion and a secondportion; and a first gate structure and a second gate structureextending along the second direction on the DDB structure.
 2. Thesemiconductor device of claim 1, wherein the first gate structureoverlaps the first portion and the DDB structure.
 3. The semiconductordevice of claim 1, wherein the second gate structure overlaps the secondportion and the DDB structure.
 4. The semiconductor device of claim 1,further comprising: a second fin-shaped structure on the second region;a single diffusion break (SDB) structure in the second fin-shapedstructure to divide the second fin-shaped structure into a third portionand a fourth portion; and a third gate structure on the SDB structure.5. The semiconductor device of claim 4, wherein the third gate structureoverlaps the third portion, the fourth portion, and the SDB structure.6. The semiconductor device of claim 4, wherein a width of the firstgate structure is equal to a width of the third gate structure.
 7. Thesemiconductor device of claim 4, wherein a width of the first gatestructure is equal to a width of the second gate structure.
 8. Thesemiconductor device of claim 1, wherein the first region comprises aNMOS region and the second region comprises a PMOS region.